Sound reproducing apparatus



N. R. KELLY SOUND REPRODUCING APPARATUS Filed Oct. 51. 1959 June so, 1942. 2,288,000

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(Ittorneg amplitude, the relay Patented June 36, 1942 UNITED STAT ES PATENT OFFICE SOUND REPRODUCING APPARATUS Norvalltay Kelly, Great Neck, N. Y., assignor to Badio Corporation of Delaware f America, a corporation Application October 31, 1939, Serial No. 302,24

' 3 Claims. (01. ire-400.4)

This invention relates to a signal cut-off relay and circuit therefor which is particularly adapted for cutting ofi the signal from such devices, for example, as a phonograph during intervals when it is desired not to reproduce sound.

The device is analogous to the ground noise reduction system used in film sound recording wherein the quantity of light striking the photo- One object of the invention is to provide a de-- vice for eliminating background noise when a sound reproducer produces sound below'a predetermined le'vel.

Another object of the invention is to provide an apparatus for eliminating background'noise in sound reproducers.

electric cell is reduced at low sound amplitudes in order to reduce ground noise. The present apparatus difiers therefrom, however, in opening the output circuit from the device when no signal of reproducible intensity is being produced.

The apparatus according to my invention is not limited to the use of phonographs, but may be used with any type of sound reproducing or transmitting circuit. In ordinary sound records,

and even in practically all audio frequency circuits, there is a definite minimum level below In the ordinary audio frequency circuit, these low level noises are transmittedand corresponding annoying sounds are reproduced. This is particularly noticeable in the broadcast of sound effects or the like where which surface'noise from a record may comparativelyvlong and where the overall amplification level from sound pickup to sound reproducer may be quite high.

In the apparatus according provide an auxiliary amplifier circuit and a re lay circuit. The relay circuit is connected into the main transmission line from the sound translating device, and the amplifier circuit which actuates the relay is connected to the sound translating device or pickup,or to an intermediate amplifier connected thereto. When the sound reaches a predetermined level corresponding to the minimum level it is desiredto reproduce, the auxiliary amplifier circuit actuates the relay, simultaneously short-circuiting the output from the sound translat'ng device and opening the link circuit from that device to the apparatus in which the sound impulses are to be used. Conversely, when the sound level reaches the desired is moved in the other direction, the short circuit is removed, and the output to my invention, I

from the soundtranslating device is again per-' nitted to pass into the link circuit.

Other and incidental objects of the invention will be apparent to those'skilled in the art from a reading of the following specification and an inspection of the accompanying drawing, in which:

The single figure is a schematic diagram of the circuit used.

An appropriate pickup or other sound translating device is indicated at ID. This device may be a magnetic phonograph pickup, as indicated, or photoelectric reproducer or microphone, or, in fact, any other source of audio frequency currents. The output from the device It) is fed into a pre-amplifier generally indicated at H, from which the sound output goes to the transformer the intervals during occur are I2, by which it is coupled to the output circuit.

In the pre-amplifier there is located a tube [3 which may be, for example, an RCA type 37.

This tube may be one of the tubes in the amplifier functioning also in its usual way, or it may be an additionaltube connected into the amplifier for the purpose of operating the apparatus of my invention. The output from this tube passes through. they coupling condenser I1 and is distributed across-the resistors l5'and IS. The lead I8 is connected between the resistors l5 and I6 and passes-to the blade IQ of a jack. When the plug 4| is not inserted in the jack, the blade I9 is connected :-with the contact 2| which, in turn, is connected 't'o ground, thereby grounding that part of .the output of the tube l3 across R. l6 when the switch circuit is not in use, allowing the entire reproducing circuit to operate in a normal manner. When the plug M is inserted in the jack, the blade I9 is moved against the contact 20, which connects this output across the potentiometer 22. This potentiometer 22 adjusts the signal level at which the relay operates to disconnect the output. The signal from across the potentiometer 22 passes through an appropriate lead ,grounded by a terminating resistor 23. to an amplifier tube 24, which is coupled by an appropriate condenser 26 and the potentiometer 21 to a second tube 28. These tubes 24 and 28 may, for example, be of the'RCA type 6F8G. Plate current is supplied from the powersupply 4? to 'sage of any signal. reaches the predetermined level, the relay 34 again moves the blade 45 passed through thecoupling condenser 30 to the tube 32 which is provided with a grid resistor 3| and a grid bias adjustment potentiometer 44. The output circuit of the tube 32 is provided with a condenser 33 of suiiicient size to bypass any audio frequency currents and thereby prevent chattering of the relay. This condenser 33 may have, for example, a capacity of 8 microfarads, and should be'of paper construction rather than electrolytic. The output from the tube 32 is connectedto the winding of the relay 34, preferably in such a fashion that when current does not pass through the relay 34 its blade 45 lies against the contact 39 and is grounded.

The transformer l2, as stated above, is connected to the output circuit. This transformer,

however, is connected to the output circuit through the Jack 35 and the contact 36 when the plug 4| is removed from the Jack and the switching mechanism is inoperative. When the plug'4l is inserted in the jack, the connection from the output side of the transformer l2 passes through the leads connectedto the plug 4|,

'the sleeve131 of the plug contacting with the 38 connecting with the spring v into contact with 43,- removing the short from the transformer and reconnecting the output circuit. f

I claim as my invention: 4

1. In combination, an electrical phonographic translating device, an output circuit 'thereior, means connected in said eutput circuit for opendetermined intensity,

ing said circuit, and means connected to said translating device and said circuit opening means for causing said circuit opening means to open when the output is below a predetermined intensity and for causing said means to close said circuit when the said output is above said presaid predetermined intensity substantially corresponding with the surface noise level of said phonographic translating device and potentiometer means for "adjusting'and changing the predetermined intensity point. I

2. In combination,.an electrical phqnographic translating device, an output circuit therefor, means connected in said output circuit for opening said circuit, and means connected to said translating, device and said circuit opening means for causing said circuit opening means to open when the output is below a predetermined intensity and for causing said means to close said circuit when the said output isabove said predetermined intensity, whereby ground noise from the phonograph record is eliminated during periods of no signal and potentiometer means for adjusting and changing the predetermined intensity point. J v

3. In combination, an input circuit, a phonographic translating device connected thereto, an output circuit, means for deriving a potential from said input circuit, an amplifier supplied with said potential and'providing an output of substantially direct current, and a relay in said output circuit connected to the output of .said

amplifier in such a manner that said output cir cuit will be open when signals in said input circuitlare below a predeterminedlevel and said output circuit will be closed when thesignals are above said predetermined level, said predetermined level substantiallycorresponding with the surface noise level of said phonographic translating device, and potentiometer means for adjusting and changing the predetermined level.

NORVAL RAY KELLY. 

